This all depends on what kind of sewer pipe you are using. If it that white garbage PVC at Home Depot that you glue together then really all you can use is sand under, over and around. It is so crappy that if you let any 3/4 gravel touch it the stuff will shatter.
I am in the process of getting an excavator and putting in a drain from my foundation to the ditch ( the joys of country living 8) because a birch tree and a lilac bush grew on top of the white PVC and then crushed it. We know this because we can see the pipe at the ditch and when we try to rod it we get stopped at the lilac bush and when we cut that root out we got stopped at the birch tree.
I use ABS only outside. If running conduit I use the gray schd 40 glue stuff. There is PVC you can use, it is quite a bit thicker and uses rubber gaskets to connect but it is harder to get.
With either of those products you can use 3/4 clear as a bed, rake it flat and then put a foot or so of 3/4 clear on top. Back fill with whatever you have to about a foot and then compact it with a jumping jack.
I see guys saying use that 4 inch white stuff with holes in it for weeping tile but the stuff is so fragile you might as well just crush it right away and bury it. Around here everyone uses Big O with the sock and I will put filter cloth around mine as well.
I tidied up the answer a bit
Very weak, brittle. Easily broken